Broken contract for 'gitLabConnection' in #961

After #916 'gitLabConnection' throws error:
```
options {
gitLabConnection('gitlab.example.com')
}
```
Error:
> "gitLabConnection" should have 3 arguments but has 1 arguments instead. @ line 58, column 7.
> gitLabConnection('gitlab.example.com')

to workaround use:

`gitLabConnection(gitLabConnection: 'gitlab.example.com', useAlternativeCredential: false, jobCredentialId: null)`

For more details see https://github.com/jenkinsci/gitlab-plugin/pull/916